1. Field of the Invention
The present invention relates generally to a communication control device, a communication apparatus, an image forming apparatus, and a computer-readable recording medium with control program instructions for the communication control device.
2. Description of the Related Art
In recent years, image processing apparatuses used for information digitization and image forming apparatuses used to output digitized information have become indispensable equipment. Such an image processing apparatus and an image forming apparatus are each configured, in many cases, as a multifunction peripheral (MFP) usable as a printer, a facsimile, a scanner, and a copier.
Such an MFP is generally connected to a communication network, such as a public switched telephone network and a facsimile communication network, via a communication line, such as a telephone line, and transmits and receives facsimile data to and from another MFP over the communication line. A technique for detecting disconnection of the communication line of the MFP is proposed and already known. An example of the technique is disclosed in Japanese Laid-open Patent Publication No. 08-070345.
Japanese Laid-open Patent Publication No. 08-070345 discloses a disconnection detection circuit that, while in an on-hook condition, measures a voltage across terminals of the communication line and detects that the communication line is disconnected when the voltage is lower than a predetermined voltage but, while in an off-hook condition, measures a current flowing through the terminals of the communication line and detects that the communication line is disconnected when the measured current is zero.
However, the disconnection detection circuit disclosed in Japanese Laid-open Patent Publication No. 08-070345 has a problem that, when connected to a communication line where the voltage across terminals of the communication line is low in the on-hook condition, the disconnection detection circuit can falsely detect that the communication line is disconnected. This problem can occur not only in an MFP but also in a communication apparatus, such as a facsimile-only apparatus and a telephone, as well.
Therefore, there is a need to increase reliability in detection of communication line's disconnection.